ALLOMETRIC GROWTH AND DNA, RNA AND TOTAL PROTEIN OF BRAINS FROM WHITE ROCK CHICKENS SELECTED FOR 56-DAY BODY-WEIGHT

Brain growth after hatch was measured in White Rock chickens selected for high (H) and low (L) body weight and their reciprocal F1 crosses. Brain weights were heavier in line H than L, however, relative to body weight brains were heavier in line L than H. Negative heterosis for brain weight caused lower allometric slopes for brain:body weight relationships in F1 than parental populations. Brain DNA unit number (total DNA/g of tissue), RNA and protein (mg/g) were similar among populations at most ages. Cellular filling generally plateaued by day 10 in all populations. Subsequent differences in brain weight were due to a greater number of cells in line H than L.